Design of Composite Floors Professor Shiming Chen School of Civil Engineering Tongji University
Design of Composite Floors Professor Shiming Chen School of Civil Engineering Tongji University
Design Example Design the primary and secondary beams of the Steel-Concrete Composite Floor. 00FS In construction stage,no temporary brace is used and the floor should be designed using elastic method. 寸 In serviceability stage,plastic method design and 3300 3300 3300 deformation calculation should be conducted. Fig.1 Composite floor structure
Design Example Design the primary and secondary beams of the Steel-Concrete Composite Floor. In construction stage, no temporary brace is used and the floor should be designed using elastic method. In serviceability stage, plastic method design and deformation calculation should be conducted. Fig. 1 Composite floor structure
Temporary Braces Floor without temporary braces: In construction stage:the steel beam bears all loads including the self-weight of composite beam and the construction live loads. In serviceability stage:the composite beam bears the subsequent dead loads and live loads. Floor with temporary braces In construction stage:the steel beam does not bear any loads,when the braces are removed,the reaction due to braces should be considered
Temporary Braces Floor without temporary braces: In construction stage: the steel beam bears all loads including the self-weight of composite beam and the construction live loads. In serviceability stage: the composite beam bears the subsequent dead loads and live loads. Floor with temporary braces In construction stage: the steel beam does not bear any loads, when the braces are removed, the reaction due to braces should be considered
Design Example Parameters: (1)terrazzo topping:30mm cast-in-situ concrete slab:100mm three-ply ceiling:0.18kN/m2 (2)standard live load:3.5kN/m2. (3)concrete:C30 steel:Q235
Design Example Parameters： （1）terrazzo topping:30mm cast-in-situ concrete slab:100mm three-ply ceiling: 0.18kN/m2 （2）standard live load:3.5kN/m2 。 （3）concrete:C30 steel: Q235
Steps ● Structure simplification ●Choosing steel beams ●Loads calculation Internal force calculation Bearing capacity:flexural capacity,vertical shear capacity shear connections ●Deflection
Steps Structure simplification Choosing steel beams Loads calculation Internal force calculation Bearing capacity：flexural capacity、vertical shear capacity、shear connections Deflection
Steps Loads calculation Loads calculation Construction Strength Serviceability Bearing design(Elastic capacity(Plastic Stage design) Stage design) deflection Deflection
Steps Serviceability Stage Loads calculation Bearing capacity(Plastic design) deflection Construction Stage Loads calculation Strength design(Elastic design) Deflection
1.Choosing beams 5400 Fig.2 Simply-supported beam (secondary beam) (1)Estimate the cross-section height of the secondary beam: h=(1/15~1/20)L =(1/15~1/20)×5400=360~270mm Take the height as h=300 mm
1.Choosing beams Fig. 2 Simply-supported beam（secondary beam） (1) Estimate the cross-section height of the secondary beam: h=(1/15~1/20) L =(1/15~1/20)×5400=360~270 mm Take the height as h=300 mm
1.Choosing beams (2)Cross-section type of the 6f=180 secondary beam Global stability: 1/b=85/10=8.5<13√235/215=14.4 082=Mu tw=10 Local stability: h/t=280/10=28<80√235/215=83.5 Cross section properties of the secondary beam Fig.3 Cross section Flange Web Cross- Moment of area area section area inertia 1800mm2 2800mm2 6400mm2 99.3×106mm4
1.Choosing beams (2) Cross-section type of the secondary beam 1 1 l b/ 85/10 8.5 13 235/ 215 14.4 0 / 280 /10 28 80 235/ 215 83.5 w h t Global stability: Local stability: Cross section properties of the secondary beam Flange area Web area Crosssection area Moment of inertia 1800mm2 2800mm2 6400mm2 99.3×106mm4 Fig.3 Cross section
2.Construction stage (loads calculation) (1)loads on secondary beams loads 标准值 Self-weight of the steel beam 78.5×6400×10-6=0.50kN/m Weight of the wet concrete slab 25×0.1×3.3=8.25kN/m Total dead load 9k=8.75kN/m Construction live load 1.0×3.3=3.3kN/m Total live load qk=3.3kN/m 9+q 5400
2.Construction stage（loads calculation） （1）loads on secondary beams loads 标准值 Self-weight of the steel beam Weight of the wet concrete slab Total dead load 78.5×6400×10-6=0.50kN/m 25×0.1×3.3=8.25kN/m gk=8.75kN/m Construction live load Total live load 1.0×3.3=3.3kN/m qk=3.3kN/m
2.Construction stage (Internal force) (2)internal forces For simply-supported beam,the bending moment and shear force under unit uniformly distributed load are as follows: 3.65 -2.70 Bending moment Shear force Fig.4
2.Construction stage（Internal force） （2）internal forces For simply-supported beam, the bending moment and shear force under unit uniformly distributed load are as follows: Bending moment Shear force Fig. 4